refactor(Dispenser): proxy-based Dispenser behind DispenserProxy

contracts/Dispenser.sol

@@ -228,6 +228,9 @@ error WrongAmount(uint256 provided, uint256 expected);
 /// @dev Caught reentrancy violation.
 error ReentrancyGuard();
 
+/// @dev The contract is already initialized.
+error AlreadyInitialized();
+
 /// @dev The contract is paused.
 error Paused();
 
@@ -263,7 +266,7 @@ contract Dispenser {
     }
 
     event OwnerUpdated(address indexed owner);
-    event TokenomicsUpdated(address indexed tokenomics);
+    event ImplementationUpdated(address indexed implementation);
     event TreasuryUpdated(address indexed treasury);
     event VoteWeightingUpdated(address indexed voteWeighting);
     event StakingParamsUpdated(uint256 maxNumClaimingEpochs, uint256 maxNumStakingTargets);
@@ -280,17 +283,29 @@ contract Dispenser {
     event AddNomineeHash(bytes32 indexed nomineeHash);
     event RemoveNomineeHash(bytes32 indexed nomineeHash);
 
+    // Dispenser proxy address slot
+    // keccak256("PROXY_DISPENSER") = "0x8bd249c73459f2c50400ebdc57436101fc7d9a76908baf1ba5be362b47b48f83"
+    bytes32 public constant PROXY_DISPENSER = 0x8bd249c73459f2c50400ebdc57436101fc7d9a76908baf1ba5be362b47b48f83;
     // Maximum chain Id as per EVM specs
     uint256 public constant MAX_EVM_CHAIN_ID = type(uint64).max / 2 - 36;
+
+    // Immutables live in the implementation bytecode, not proxy storage: they are re-settable by deploying
+    // a new implementation and calling changeImplementation. Every new implementation deploy must pass the
+    // correct constructor args — a wrong value silently rewires the proxy.
     uint256 public immutable defaultMinStakingWeight;
     uint256 public immutable defaultMaxStakingIncentive;
     // OLAS token address
     address public immutable olas;
+    // Tokenomics proxy address (stable by construction — the proxy address never changes)
+    address public immutable tokenomics;
     // Retainer address in bytes32 form
     bytes32 public immutable retainer;
     // Retainer hash of a Nominee struct composed of retainer address with block.chainid
     bytes32 public immutable retainerHash;
 
+    // Storage layout below is consumed via the DispenserProxy delegatecall and is FROZEN: never remove,
+    // reorder, retype or insert in the middle — new variables are appended strictly after the last mapping.
+
     // Max number of epochs to claim staking incentives for
     uint256 public maxNumClaimingEpochs;
     // Max number of targets for a specific chain to claim staking incentives for
@@ -302,8 +317,6 @@ contract Dispenser {
     // Pause state
     Pause public paused;
 
-    // Tokenomics contract address
-    address public tokenomics;
     // Treasury contract address
     address public treasury;
     // Vote Weighting contract address
@@ -320,36 +333,27 @@ contract Dispenser {
     // Mapping for epoch number => refunded all the staking inflation due to zero total voting power
     mapping(uint256 => bool) public mapZeroWeightEpochRefunded;
 
-    /// @dev Dispenser constructor.
+    /// @dev Dispenser implementation constructor: sets the implementation-bytecode immutables only.
+    /// @notice The mutable state is set via initialize() delegatecall-ed by the DispenserProxy constructor.
     /// @param _olas OLAS token address.
-    /// @param _tokenomics Tokenomics address.
-    /// @param _treasury Treasury address.
-    /// @param _voteWeighting Vote Weighting address.
+    /// @param _tokenomics Tokenomics proxy address.
+    /// @param _retainer Retainer address in bytes32 form.
+    /// @param _defaultMinStakingWeight Default min staking weight (bounded by uint16).
+    /// @param _defaultMaxStakingIncentive Default max staking incentive (bounded by uint96).
     constructor(
         address _olas,
         address _tokenomics,
-        address _treasury,
-        address _voteWeighting,
         bytes32 _retainer,
-        uint256 _maxNumClaimingEpochs,
-        uint256 _maxNumStakingTargets,
         uint256 _defaultMinStakingWeight,
         uint256 _defaultMaxStakingIncentive
     ) {
-        owner = msg.sender;
-        _locked = 1;
-        // Staking incentives must be paused at the time of deployment because staking parameters are not live yet
-        paused = Pause.StakingIncentivesPaused;
-
         // Check for at least one zero contract address
-        if (_olas == address(0) || _tokenomics == address(0) || _treasury == address(0) ||
-            _voteWeighting == address(0) || _retainer == 0) {
+        if (_olas == address(0) || _tokenomics == address(0) || _retainer == 0) {
             revert ZeroAddress();
         }
 
         // Check for zero value staking parameters
-        if (_maxNumClaimingEpochs == 0 || _maxNumStakingTargets == 0 || _defaultMinStakingWeight == 0 ||
-            _defaultMaxStakingIncentive == 0) {
+        if (_defaultMinStakingWeight == 0 || _defaultMaxStakingIncentive == 0) {
             revert ZeroValue();
         }
 
@@ -363,17 +367,71 @@ contract Dispenser {
 
         olas = _olas;
         tokenomics = _tokenomics;
-        treasury = _treasury;
-        voteWeighting = _voteWeighting;
 
         retainer = _retainer;
         retainerHash = keccak256(abi.encode(IVoteWeighting.Nominee(retainer, block.chainid)));
-        maxNumClaimingEpochs = _maxNumClaimingEpochs;
-        maxNumStakingTargets = _maxNumStakingTargets;
         defaultMinStakingWeight = _defaultMinStakingWeight;
         defaultMaxStakingIncentive = _defaultMaxStakingIncentive;
     }
 
+    /// @dev Initializes the dispenser proxy storage.
+    /// @notice Delegatecall-ed by the DispenserProxy constructor; the caller becomes the owner.
+    /// @param _treasury Treasury address.
+    /// @param _voteWeighting Vote Weighting address.
+    /// @param _maxNumClaimingEpochs Maximum number of epochs to claim staking incentives for.
+    /// @param _maxNumStakingTargets Maximum number of staking targets on a single chain Id.
+    function initialize(
+        address _treasury,
+        address _voteWeighting,
+        uint256 _maxNumClaimingEpochs,
+        uint256 _maxNumStakingTargets
+    ) external {
+        // Check that the proxy storage has not been initialized yet
+        if (owner != address(0)) {
+            revert AlreadyInitialized();
+        }
+
+        // Check for at least one zero contract address
+        if (_treasury == address(0) || _voteWeighting == address(0)) {
+            revert ZeroAddress();
+        }
+
+        // Check for zero value staking parameters
+        if (_maxNumClaimingEpochs == 0 || _maxNumStakingTargets == 0) {
+            revert ZeroValue();
+        }
+
+        owner = msg.sender;
+        _locked = 1;
+        // Staking incentives must be paused at the time of deployment because staking parameters are not live yet
+        paused = Pause.StakingIncentivesPaused;
+
+        treasury = _treasury;
+        voteWeighting = _voteWeighting;
+        maxNumClaimingEpochs = _maxNumClaimingEpochs;
+        maxNumStakingTargets = _maxNumStakingTargets;
+    }
+
+    /// @dev Changes the dispenser implementation contract address behind the proxy.
+    /// @param implementation Dispenser implementation contract address.
+    function changeImplementation(address implementation) external {
+        // Check for the contract ownership
+        if (msg.sender != owner) {
+            revert OwnerOnly(msg.sender, owner);
+        }
+
+        // Check for the zero address
+        if (implementation == address(0)) {
+            revert ZeroAddress();
+        }
+
+        // Store the implementation address under the designated storage slot
+        assembly {
+            sstore(PROXY_DISPENSER, implementation)
+        }
+        emit ImplementationUpdated(implementation);
+    }
+
     /// @dev Checkpoints specified staking target (nominee in Vote Weighting) and gets claimed epoch counters.
     /// @param nomineeHash Hash of a Nominee(stakingTarget, chainId).
     /// @param numClaimedEpochs Specified number of claimed epochs.
@@ -685,21 +743,16 @@ contract Dispenser {
     }
 
     /// @dev Changes various managing contract addresses.
-    /// @param _tokenomics Tokenomics address.
+    /// @notice The tokenomics address is an implementation immutable (it points at the stable TokenomicsProxy);
+    ///         changing it requires deploying a new implementation and calling changeImplementation.
     /// @param _treasury Treasury address.
     /// @param _voteWeighting Vote Weighting address.
-    function changeManagers(address _tokenomics, address _treasury, address _voteWeighting) external {
+    function changeManagers(address _treasury, address _voteWeighting) external {
         // Check for the contract ownership
         if (msg.sender != owner) {
             revert OwnerOnly(msg.sender, owner);
         }
 
-        // Change Tokenomics contract address
-        if (_tokenomics != address(0)) {
-            tokenomics = _tokenomics;
-            emit TokenomicsUpdated(_tokenomics);
-        }
-
         // Change Treasury contract address
         if (_treasury != address(0)) {
             treasury = _treasury;

contracts/proxies/DispenserProxy.sol

@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.25;
+
+/// @dev Proxy initialization failed.
+error InitializationFailed();
+
+/// @dev Zero address.
+error ZeroAddress();
+
+/// @dev Zero Value.
+error ZeroValue();
+
+/*
+* This is a proxy contract for dispenser.
+* Proxy implementation is created based on the Universal Upgradeable Proxy Standard (UUPS) EIP-1822.
+* The implementation address must be located in a unique storage slot of the proxy contract.
+* The upgrade logic must be located in the implementation contract.
+* Special dispenser implementation address slot is produced by hashing the "PROXY_DISPENSER" string
+* in order to make the slot unique.
+* The fallback() implementation for all the delegatecall-s is inspired by the Gnosis Safe set of contracts.
+*/
+
+/// @title DispenserProxy - Smart contract for dispenser proxy
+/// @author Aleksandr Kuperman - <aleksandr.kuperman@valory.xyz>
+/// @author Andrey Lebedev - <andrey.lebedev@valory.xyz>
+contract DispenserProxy {
+    // Code position in storage is keccak256("PROXY_DISPENSER") = "0x8bd249c73459f2c50400ebdc57436101fc7d9a76908baf1ba5be362b47b48f83"
+    bytes32 public constant PROXY_DISPENSER = 0x8bd249c73459f2c50400ebdc57436101fc7d9a76908baf1ba5be362b47b48f83;
+
+    /// @dev DispenserProxy constructor.
+    /// @param dispenser Dispenser implementation address.
+    /// @param dispenserData Dispenser initialization data.
+    constructor(address dispenser, bytes memory dispenserData) {
+        // Check for the zero address, since the delegatecall works even with the zero one
+        if (dispenser == address(0)) {
+            revert ZeroAddress();
+        }
+
+        // Check for the zero data
+        if (dispenserData.length == 0) {
+            revert ZeroValue();
+        }
+
+        assembly {
+            sstore(PROXY_DISPENSER, dispenser)
+        }
+        // Initialize proxy dispenser storage
+        (bool success, ) = dispenser.delegatecall(dispenserData);
+        if (!success) {
+            revert InitializationFailed();
+        }
+    }
+
+    /// @dev Delegatecall to all the incoming data.
+    fallback() external payable {
+        assembly {
+            let dispenser := sload(PROXY_DISPENSER)
+            // Otherwise continue with the delegatecall to the dispenser implementation
+            calldatacopy(0, 0, calldatasize())
+            let success := delegatecall(gas(), dispenser, 0, calldatasize(), 0, 0)
+            returndatacopy(0, 0, returndatasize())
+            if eq(success, 0) {
+                revert(0, returndatasize())
+            }
+            return(0, returndatasize())
+        }
+    }
+}

test/Dispenser.t.sol

@@ -3,6 +3,7 @@ pragma solidity ^0.8.30;
 import {Test} from "forge-std/Test.sol";
 import {Utils} from "./utils/Utils.sol";
 import {Dispenser} from "../contracts/Dispenser.sol";
+import {DispenserProxy} from "../contracts/proxies/DispenserProxy.sol";
 import "../contracts/Tokenomics.sol";
 import {TokenomicsProxy} from "../contracts/proxies/TokenomicsProxy.sol";
 import {Treasury} from "../contracts/Treasury.sol";
@@ -56,24 +57,32 @@ contract BaseSetup is Test {
         componentRegistry = new MockRegistry();
         agentRegistry = new MockRegistry();
         serviceRegistry = new MockRegistry();
-        dispenser = new Dispenser(address(olas), deployer, deployer, deployer, retainer, 100, 100, 100, 1 ether);
 
-        // Depository contract is irrelevant here, so we are using a deployer's address
-        // Correct tokenomics address will be added below
-        treasury = new Treasury(address(olas), deployer, deployer, address(dispenser));
+        // Depository and dispenser contracts are irrelevant at this point, so we are using a deployer's address
+        // Correct tokenomics and dispenser addresses will be added below
+        treasury = new Treasury(address(olas), deployer, deployer, deployer);
 
         Tokenomics tokenomicsMaster = new Tokenomics();
         // Depository contract is irrelevant here, so we are using a deployer's address
+        // Dispenser address is a placeholder until the dispenser proxy is deployed below
         bytes memory proxyData = abi.encodeWithSelector(tokenomicsMaster.initializeTokenomics.selector,
-            address(olas), address(treasury), deployer, address(dispenser), address(ve), epochLen,
+            address(olas), address(treasury), deployer, deployer, address(ve), epochLen,
             address(componentRegistry), address(agentRegistry), address(serviceRegistry), address(0));
         TokenomicsProxy tokenomicsProxy = new TokenomicsProxy(address(tokenomicsMaster), proxyData);
         tokenomics = Tokenomics(address(tokenomicsProxy));
 
-        // Change tokenomics address
-        treasury.changeManagers(address(tokenomics), address(0), address(0));
-        // Change the tokenomics and treasury addresses in the dispenser to correct ones
-        dispenser.changeManagers(address(tokenomics), address(treasury), address(0));
+        // Deploy dispenser implementation (tokenomics proxy address is an implementation immutable) and proxy
+        // Vote Weighting contract is irrelevant here, so we are using a deployer's address
+        Dispenser dispenserMaster = new Dispenser(address(olas), address(tokenomics), retainer, 100, 1 ether);
+        bytes memory dispenserData = abi.encodeWithSelector(dispenserMaster.initialize.selector,
+            address(treasury), deployer, 100, 100);
+        DispenserProxy dispenserProxy = new DispenserProxy(address(dispenserMaster), dispenserData);
+        dispenser = Dispenser(address(dispenserProxy));
+
+        // Change tokenomics and dispenser addresses in treasury
+        treasury.changeManagers(address(tokenomics), address(0), address(dispenser));
+        // Change the dispenser address in tokenomics to the correct one
+        tokenomics.changeManagers(address(0), address(0), address(dispenser));
 
         // Set treasury contract as a minter for OLAS
         olas.changeMinter(address(treasury));